The present invention relates to optical-quality polarized parts, and, in particular, to variable transmission polarized lenses for use in sunglasses, visors and the like. In particular, the present invention is directed at lenses comprising a polarizing film integrally bonded within a polyurethanic material which itself comprises a photochromic compound therein.
Optical-quality eyewear requires good optical performance. In the selection of lens materials for use in optical-quality eyewear, the color, weight, and safety of the material is important, as well as good optical performance. Most often, however, the respective properties of different materials necessitate trade-offs among the desired lens characteristics. For instance, glass has very good optical properties, but it is heavy (a dense material) and only impact resistant if thick (resulting in an even heavier lens). Polymeric thermoset resins, such as CR-39, are lighter in weight but are lacking in impact resistance. Polycarbonate, in contrast, is both lightweight and highly impact resistant. Polycarbonate also has a high refractive index. Thus, thinner lenses can be made utilizing polycarbonate. However, due to lower Abbe Number, polycarbonate exhibits more chromatic aberration than glass, typically resulting in unacceptable off-axis distortion.
Polyurethanic materials have also been used as a lens material. U.S. Pat. No. 5,962,617 (Simula) and Published Patent Application No. US 2001/0028435 (Younger Optics), each of which are incorporated herein by reference, describe a polyurethanic resin material for use in lenses. This material comprises the reaction product of a pre-polymer composition and a diamine curing agent. As described in these references, this material may offer improved lens characteristics over conventional materials.
Another type of lenses are photochromic lenses. Photochromic lenses adapt their transmission to a variable light intensity by balancing colors and helping keep the brightness on the eyes constant. Photochromic lenses are also often useful when a big change of luminous intensity take place. This can happen, for example, by simply getting out of the car into the sunshine, and during open air activities such as on high mountains and at seaside resorts. Photochromic compounds, contained in a photochromic lens, exhibit a reversible change in color when exposed to light radiation involving ultraviolet rays, such as the ultraviolet radiation in sunlight or the light of a mercury lamp. Various classes of photochromic compounds have been synthesized for use in applications in which a sunlight-induced reversible color change or darkening is desired. The most widely described classes of photochromic compounds are spyro-oxazines, spyro-pyrans and fulgides.
The general mechanism responsible for the reversible change in color, i.e., a change in the absorption spectrum in the visible range of light (400–700 nm) exhibited by different types of photochromic compounds has been described and categorized. See John C. Crano, “Chromogenic Materials (Photochromic)”, Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, 1993, pp. 321–332, incorporated herein by reference. The general mechanism for the most common classes of photochromic compounds involves an electronic mechanism causing the transformation of a colorless open ring form into a colored closed ring form.
In the aforedescribed mechanisms, the photochromic compounds require an environment in which they can reversibly transform. In solid polymer matrices, the rates at which the photochromic processes of activation, i.e., formation of color or darkening, and fading, i.e., the return to the original or colorless state, occur are believed to be dependent on the free volume in the polymer matrix. The free volume of the polymer matrix is dependent upon the flexibility of the chain segments of the polymer environment surrounding the photochromic compound, i.e., the local mobility or local viscosity of the chain segments comprising the matrix. See Claus D. Eisenbach, “New Aspects of Photochromism in Bulk Polymers”, Photographic Science and Engineering, 1979, pp. 183–190, incorporated herein by reference. One of the main obstacles reported by Claus D. Eisenbach, for the larger commercial application of photochromic systems, is the slow rate of photochromic activation and fade in a solid polymer matrix.
The use of photochromic compounds in polyurethanes to produce optical articles has been described in U.S. Published Patent Application 2001/0050356, and references cited therein, which are each incorporated herein by reference.
Polarized lenses and visors are widely used for glare reducing optical devices and are especially suitable for sport activities taking place outdoors, generally in snow, water and sand environments. Polarized lenses are also highly appreciated for driving activity because they can reduce glare and provide better vision of the automobile instrumentation panel as well as the roadway
Generally, polarized lenses are obtained by bonding a polarized film onto the plastic lens surface or introducing such film into the plastic material during the polymerization. Regardless of which particular material is used for the lens body, it is preferable in many applications to incorporate a polarizing film into the lens. However, while polarizing films have been used in combination with many of the prior art lens body materials, none of the photochromic polyurethanes disclosed in the prior art teach or even suggest the use of a polarizing film in combination with the photochromic polyurethanes.
Accordingly, there is a need in the field for lenses which are both polarized to reduce the glare and which provide the wearer with a variable perception depending on the light variation. The present invention overcomes shortcomings of the prior art and is directed at the use of photochromic compounds in a polyurethanic material incorporating a polarizing film.